1. Field of the Invention
The present invention relates to a non-asbestos friction material. In particular, the present invention relates to a friction material for use in industrial equipments, railcars, baggage cars and passenger cars, which is improved in balance controlling performance between wear resistance, preventing ability of metal catch, cracking resistance, and braking ability. Particularly, the present invention relates to a friction material capable of preventing environmental pollution by not containing metals and metallic compounds. More specifically, the invention relates to brake pads, brake linings and clutch facings for use in the above uses.
2. Related Art
Friction materials for use in brakes such as disc brakes and drum brakes or clutches include a friction modifier for giving friction ability and controlling the friction ability, a fibrous material for reinforcement, and a binder to integrate these components. Of these materials, the fibrous material may include the kinds of a metallic fibers an inorganic fiber, and an organic fiber. These fibers have respective characteristics and one kind alone cannot satisfy all the requirements, so that two or more kinds are usually used in combination.
On the other hand, as materials for controlling friction characteristics of the friction material, there are the friction modifier and a solid lubricant. These materials also include inorganic and organic materials, and they have respective characteristics and one kind alone cannot satisfy all the requirements, so that they are usually used in combination of two or more kinds. As the examples of friction modifiers, inorganic friction modifiers, e.g., alumina, silica, magnesia, zirconia, chromium oxide, quartz, etc., and organic friction modifiers, e.g., synthetic rubber, cashew resin, etc, are exemplified. As solid lubricants, e.g., graphite, molybdenum disulfide, etc., are exemplified.
As fillers, barium sulfate, calcium carbonate, metallic powder, vermiculite, mica and the like are used.
As friction materials obtained by blending these ingredients capable of restraining the attack on the mating member, and improved in fading resistance and wear resistance, non-asbestos friction materials of various kinds of blending are suggested.
Various advantages can be obtained by blending a metal in the form of a metallic fiber or metallic powder into the friction material, such that structural reinforcement may be achieved, adhesive frictional force by transfer to the mating member may be obtained, high thermal conductivity and heat radiation may be ensured, so that various kinds of metals have been used hitherto.
However, various environmental problems caused by these metals are posed in these days such as pollution of river and ocean, harmful effect on human body and the like, and the countermeasures are now required.
As an example of the countermeasures, JP-A-2004-155843 discloses a non-asbestos friction material manufactured by molding a non-asbestos friction material composition mainly including a fibrous material containing at least a steel fiber excluding asbestos, a binder, and a filler, and curing the molded product, wherein a petroleum coke having an average particle size of from 50 to 150 μm and hard inorganic particles having an average particle size of from 5 to 30 μm are contained. JP-A-2004-155843 discloses that the non-asbestos friction material is capable of responding to the requirements of customers for the latest friction material increased in performance, light weight, miniaturization, and low costs, and is well balanced in wear resistance and friction coefficient and, further, hardly accompanied by squeaky noise and foreign sound at the time of braking. However, as is clearly shown in Examples 1 to 5 of Table 1 of JP-A-2004-155843, since this non-asbestos friction material contains 10 vol % of copper powder, there is the possibility of causing harmful influences on human body and environment.
Similarly, JP-A-58-061169 discloses a non-asbestos friction material composition suitable for use as a friction element essentially including a thermosetting binder, a fibrous reinforcing material, and Aramid polymer pulp fiber in an effective amount to form good structural integrity of the preform manufactured from the friction material, which is a friction material improved in bending strength, friction coefficient and wear resistance. However, the friction material composition contains a copper fiber and a brass fiber or copper and brass as the metal powders, so that there is the possibility of causing harmful influences on human body and environment similarly to JP-A-2004-155843.
Further, for the purpose of securing wear resistance at high temperature high load, the friction material contains metal sulfide.
However, certain kinds of metal sulfides are ascertained to have influences on human body and environment, and further expensive, so that disadvantageous from the aspect of manufacturing costs.
For the purpose of providing a friction material for brake not containing materials containing heavy metals such as Cu, antimony and the like, JP-A-2002-138273 discloses the technique of manufacturing a friction material for brake containing a fiber component, a binding component and a friction controlling component, wherein magnesium oxide (MgO) and graphite are contained in the friction material in an amount of from 45 to 80 vol %, and the volume ratio of the magnesium oxide to graphite (MgO/graphite) is from 1/1 to 4/1.
JP-A-2002-138273 discloses that the invention can provide a friction material for brake having high temperature friction performance and mechanical characteristics the same or higher than those of conventional non-asbestos friction materials even when heavy metals and heavy metal compounds such as a Cu fiber, Cu powder and Sb2S3 powder are not contained.